1. Field of the Invention
The present invention relates to surface treated metallic materials and a manufacturing method thereof, used in electronic and electrical components, which offers improved adhesion between a substrate such as an electronic or electrical component in which at least the surface is metallic, and a resin, wherein the improved adhesion is achieved by forming on the surface of the substrate a metallic compound layer comprising a mesh of minute cracks, or a scaly or squamate metallic compound layer formed from a plurality of upright protrusions.
2. Description of the Related Art
In electronic and electrical components such as lead frames, printed circuit boards, and fixed configurations of semiconductor elements and radiators, many bonding interfaces exist between metals and resins, and this type of bonding interface has been prone to peeling. Particularly in those cases where thermosetting resins such as epoxy resins and polyimide resins or thermoplastic resins with high molding temperatures are used, because the entire component needs to be exposed to high temperatures of 200xcx9c300xc2x0 C. in order to mold the resin, if the adhesion between the resin and the metallic surface is poor then water adsorbed into the surface of the metal can expand aiding the separation of the resin from the metallic surface, and the resin may crack and air bubbles called blisters form, which not only lowers the corrosion resistance of the inner component, but can also damage the elemental structure inside the component. Consequently, improving the adhesion between metal and resin is extremely important in the production of reliable electronic and electrical components.
Using mechanical means to form holes in, or roughen the surface of the metal is an effective technique for improving the adhesion between metal and resin, but this type of mechanical processing is very expensive. Consequently, a variety of experiments have been conducted into surface treatments of particularly the metal surface in order to improve resin adhesion.
One such surface treatment is known as xe2x80x9cblack oxide finishxe2x80x9d, and can only be used on copper and copper alloys. In order to create a black oxide finish, a metallic component of copper or a copper alloy is immersed in a strongly alkali solution and boiled, which generates minute fibrous deposits uniformly across the surface of the metallic component, making the surface appear velvet-like. The fibrous deposits are cuprous oxide, and forming a resin layer on to the thus treated metallic surface produces greater bonding strength than that observed in the case of untreated metal.
However the treated surface obtained through black oxide finish treatment lacks durability, and the bonding strength with resin decreases over time, or on heat treatment. Furthermore, if the resin used is a particularly hard resin such as PEEK (polyether ether ketone) then the fibrous deposits on the treated surface are broken down leading to peeling of the resin layer. Because of these problems, black oxide finish treatment can not be used on valuable precision components or when high levels of reliability are required.
Other treatment methods also exist for improving the adhesion of the metal and resin. For example in Japanese Patent Application, First Publication No. Hei-9-209167 a technique is disclosed whereby in order to increase the adhesion between a metallic parent material and a molded resin, the parent material is first immersed in a solution incorporating hexavalent chromic acid, resulting in the formation of a thin oxide film incorporating trivalent chromium on the parent material surface. The plating solution disclosed in the documentation comprised for example 1xcx9c10% CrO3 and 0.1xcx9c1% of sulfuric acid or nitric acid, and a copper plate was immersed in the plating solution at 20xcx9c50xc2x0 C. for a period of 10xcx9c60 seconds, without passing any current through the solution, to form the oxide film. It was disclosed in the documentation that if the immersion time was greater than 60 seconds then the oxide film became too thick. Further experiments by the inventors of the present invention revealed that the oxide film formed under the above conditions had a smooth surface.
Furthermore in Japanese Patent Application, First Publication No. Hei-9-172125 a technique is disclosed whereby in order to improve the adhesion between a lead frame and a resin package, a chromium/zinc mixture in which the zinc:chromium ratio was greater than approximately 4:1 was formed on the surface of the lead frame. The thickness of the mixture film should preferably be 10xcx9c1000 angstroms, with layers of thickness 40xcx9c80 angstroms (0.04xcx9c0.08 xcexcm) being most desirable. The treatment solution detailed in the documentation incorporates hydroxide ions, 0.07xcx9c7 g/l zinc ions, and 0.1xcx9c100 g/l of a hexavalent chromium salt, and the lead frame is electroplated in this solution to generate the surface film. Further experiments by the inventors of the present invention revealed that a film of thickness 0.04xcx9c0.08 xcexcm formed under the above conditions was quite fine and had a smooth surface, and did not display very good bonding strength to resin.
Following much research into surface treatment methods for metallic plates the inventors of the present invention discovered that the addition of a strontium salt to a chrome plating solution resulted in the formation of a layer with a previously unknown, unusual surface structure. The layer is thicker than either of the two films described above and has a fine mesh pattern of cracks on the surface. Common sense would suggest that when such cracks are formed the sections surrounding the cracks would peel away like scales, but the experiments by the inventors showed that the cracked surface was resistant to peeling from the metal surface, and moreover displayed a large increase in bonding strength on binding to a resin.
The present invention is based on the above findings, and aims to provide surface treated metallic materials and electronic and electrical components which display good adhesion to resin.
In order to achieve the above aim, a surface treated metallic material according to the present invention comprises a substrate in which at least the surface thereof is made of metal, and a metallic compound layer which is formed on at least a portion of the substrate surface, wherein a mesh pattern of minute cracks is formed across the entire surface of the metallic compound layer.
With the present invention, because the surface of the metallic compound layer positioned between the metallic substrate and the resin adhesive layer is formed of a fine mesh of cracks, a portion of the resin adhesive layer flows down into the cracks creating an anchoring effect and binding the two layers strongly together. Consequently, it is possible to markedly improve the bonding strength between the metallic compound layer and the resin adhesive layer.
Furthermore, in a manufacturing method of a surface treated metallic material according to the present invention, a substrate in which at least the surface thereof is made of metal is brought in contact with a plating solution incorporating a strontium salt and either one, or two or more of, the materials selected from the group consisting of chromic acid, niobic acid, rhodic acid, vanadic acid, palladic acid, nickelic acid, and the various salts thereof, and where by subsequently passing a current through the plating solution and making the surface of the substrate the cathode, a metallic compound layer, the entire surface of which is covered by a mesh of minute cracks, is formed on the surface of the substrate.
Moreover, an electronic or electrical component according to the present invention is provided with a surface treated metallic material, which comprises a substrate in which at least the surface thereof is made of metal, and a metallic compound layer which is formed on at least a portion of the substrate surface and in which a mesh pattern of fine cracks is formed across the entire surface thereof, and with a resin layer which is formed on top of the metallic compound layer.
The inventors also discovered that by using a plating solution incorporating one, or two or more of, the materials selected from the group consisting of chromic acid, niobic acid, rhodic acid, vanadic acid, palladic acid, nickelic acid, and the various salts thereof, and then carrying out electroplating at a higher cathode current density than normal, a plurality of upright protrusions in a scale like pattern were formed on the surface of the layer generated. Common sense would suggest that when such scaly protrusions are formed the protrusions would peel away like scales, but the experiments by the inventors showed that the scaly protrusions were resistant to peeling from the metal surface, and moreover displayed a large increase in bonding strength on binding to a resin.
A second surface treated metallic material according to the present invention comprises a substrate in which at least the surface thereof is made of metal, and a metallic compound layer which is formed on at least a portion of the substrate surface, wherein a scale like pattern of a plurality of upright protrusions is formed on the surface of the metallic compound layer.
With such a surface treated metallic material, because the surface of the metallic compound layer positioned between the metallic substrate and the resin adhesive layer is formed of fine scale like protrusions, a portion of the resin adhesive layer flows down inside the scale like protrusions creating an anchoring effect and binding the two layers strongly together. Consequently, it is possible to markedly improve the bonding strength between the metallic compound layer and the resin adhesive layer.
Moreover the second surface treated metallic material according to the present invention can also be formed comprising a substrate in which at least the surface thereof is made of copper or a copper alloy, a chromium compound layer which is formed on at least a portion of the substrate surface, and an intermediate layer incorporating copper and chromium which is formed between the chromium compound layer and the substrate, wherein a scale like pattern of a plurality of upright protrusions of the chromium compound is formed on the surface of the chromium compound layer.
In a manufacturing method of the second surface treated metallic material according to the present invention, a substrate in which at least the surface thereof is made of metal is brought in contact with a plating solution incorporating one, or two or more of, the materials selected from the group consisting of chromic acid, niobic acid, rhodic acid, vanadic acid, palladic acid, and the various salts thereof, and by passing a current of cathode current density of 2xcx9c20 A/dm2 through the plating solution and making the surface of the substrate the cathode, a metallic compound layer, the entire surface of which is covered by a mesh of fine scale like protrusions, is formed on the surface of the substrate.
Furthermore, in another manufacturing method, a substrate in which at least the surface thereof is made of metal is brought in contact with a plating solution incorporating nickelic acid, and by passing a current of cathode current density of 0.01xcx9c10 A/dm2 through the plating solution and making the surface of the substrate the cathode, a metallic compound layer, the entire surface of which is covered by a mesh of fine scale like protrusions, is formed on the surface of the substrate.
Another electronic or electrical component according to the present invention is provided with a surface treated metallic material, comprising a substrate in which at least the surface thereof is made of metal, and a metallic compound layer which is formed on at least a portion of the substrate surface and in which a scale like pattern of a plurality of upright protrusions is formed across the surface thereof, and with a resin layer which is formed on top of said metallic compound layer.